Unwanted by-products of producing livestock include the inherent odors, particularly those created by livestock waste. Livestock waste emits foul and noxious gases, including hydrogen sulfide and ammonia. Not only are these gases unpleasant and potentially dangerous for those who are located near waste collection areas, but many regulatory bodies regulate the permitted emissions of certain gases from an agricultural operation. Further, some regulatory bodies require larger agricultural operations to provide air emission plans, which include methods and practices that will be employed by the agricultural operations to minimize emissions of certain gases and procedures to respond to complaints directed at the facility, including identifying strategies to address the sources of odors and noxious gases. Compounding the problem is that agricultural businesses are often subjected to difficult market conditions, requiring that the livestock producer hold down costs.
Various strategies can be employed to reduce emissions. One alternative, described in U.S. patent application Ser. No. 11/155,669, incorporated herein by reference in its entirety, is to suppress or neutralize odors within a manure pit of an agricultural building. While this alternative works to suppress odors beneath the building, the odorous gases may also still need to be evacuated at some point in the future.
Another approach is to attempt to filter gases from exhaust air after it has been evacuated from the building. One known approach is to employ so-called biofilter materials as a filtration media. Biofiltration employs microorganisms present within biodegradable materials to break down gaseous contaminants and reduce the amount of hydrogen sulfide and ammonia present in exhaust air. Prior approaches port exhaust air from an agricultural building into an air plenum located below a field of biofilter material. As the exhaust air is forced into the plenum, the resulting pressure forces the air through the field. However, forcing air through a thick field of biofilter material creates head loss on the exhaust fan, resulting in a need for more a powerful exhaust fan. Further, a number of other factors, including the particular choice of biofilter material and the settling of biofilter material over time can exacerbate the head loss. In addition, a phenomenon known as channeling, which is the shifting of material across the field, can create localized areas within the field with reduced humidity as more air passes through areas with a smaller concentration of material. Reduced humidity can result in reduced microorganism activity, which unfortunately reduces the filtering capability of the field. In addition, it is recommended that biofilter fields be located on sloping, well-drained land to control the amount of moisture the field of biofilter material, thereby limiting where biofilter fields can be employed.
What is needed then, is an effective way to reduce the emission levels of odorous and noxious gases of exhaust air from agricultural applications, such as the exhaust air from agricultural livestock buildings. The solution should result in minimal head loss on the exhaust fan, be easily maintained, employable in a large number of applications, and should be relatively inexpensive.